WASHINGTON—After some initial bickering, federal regulators agree that antitrust law should play a role, albeit limited, over the conduct of initial public offerings.

In a new brief to the U.S. Supreme Court on Jan. 22, the U.S. Department of Justice’s Antitrust Division and the Federal Trade Commission (FTC) have joined with the Securities and Exchange Commission (SEC) in support of a unified position on regulation of IPOs. To ease tension among the regulators, the three agencies are telling the Supreme Court that there should be narrow antitrust oversight of IPOs but the SEC should remain the primary overseer.